Tonometers are well-known devices for detecting the intraocular pressure within an eye. There are several types of tonometers available. In general, the commercially available tonometers require that the eyelid be open and the device contact directly or indirectly the open eye. For example, one type of tonometer uses a jet of gas that impinges against the open eye. Another type has a probe that makes physical contact with the open eye. Such conventional tonometers are expensive, and not particularly accurate. Moreover, their use frequently irritates to the patient's eye. Consequently, it would be desirable to provide a tonometer that could detect the intraocular pressure through the closed eyelid of a patient. Furthermore, it would be desirable to provide an inexpensive device which patients could use themselves.